Inhibition of Respiratory Burst Activity in Alveolar Macrophages by Bisbenzylisoquinoline Alkaloids: Characterization of Drug-Cell Interaction

The objective of this study was to investigate the effects of various bisbenzylisoquinoline (BBIQ) alkaloids on respiratory burst activity of alveolar macrophages and to characterize the interaction of these drugs with alveolar phagocytes. BBIQ alkaloids were chosen for study because they exhibit a wide range of antifibrotic potencies in a rat model, with tetrandrine being very effective and tubocurarine being ineffective. These drugs inhibited zymosan-stimulated oxygen consumption with a potency sequence of tetrandrine (TT) approximately fangchinoline (FA) > berbamine (BE) approximately cepharanthine (CE) approximately cycleanine (CY) >> tubocurarine (TU). This inhibition of respiratory burst activity could not be attributed to a drug-induced decline in the ATP content of these pneumocytes. Drug binding to alveolar macrophages was directly dependent on temperature and drug concentration. The sequence for binding capacity was FA > TT approximately BE approximately CY > CE >> TU. Therefore, there was no simple relationship between binding capacity and inhibitory potency. Binding capacity was not related to lipophilicity of these alkaloids. In addition, tetrandrine failed to bind to metabolically dead cells or sonicated macrophage preparations. These data suggest that the interaction of BBIQ alkaloids with phagocytes is not simply nonspecific binding to membrane lipids. Alteration of the cytoskeletal system with vinblastine, taxol, or cytochalasin B decreased tetrandrine binding by approximately 33% when added separately and by 93% when added jointly. Pre-exposure of alveolar macrophages to stimulants increased the ability of BBIQ alkaloids to inhibit both oxygen consumption and superoxide release. These data suggest that the mechanism by which BBIQ alkaloids inhibit activation of phagocytes involves microtubules and bules and microfilaments. Pre-exposure of macrophages to stimulants would change the conformation of cytoskeletal components and may make these structures more susceptible to drug interaction.

Effects of exposure to diesel exhaust particles (DEP) on pulmonary metabolic activation of mutagenic agents

Exposure of rats to diesel exhaust particles (DEP) or carbon black (CB) has been shown to induce time-dependent changes in CYP1A1and CYP2B1 in the lung. The present study evaluated the role of these metabolic enzymes on the pulmonary bioactivation of mutagens. Male Sprague-Dawley rats were intratracheally instilled with saline (control), DEP or CB (35 mg/kg body weight) and sacrificed at 1, 3, or 7 days post-exposure. Both control and exposed lung S9 increased the mutagenic activity of 2-aminoanthracene (2-AA), 2-aminofluorene (2-AF), 1-nitropyrene (1-NP), and the organic extract of DEP (DEPE) in Ames tests with Salmonella typhimurium YG1024 in a dose-dependent manner. Lung microsomes prepared form control or particle-exposed S9, but not cytosolic protein, activated 2-AA mutagenicity. Compared to saline controls, CB-exposed S9 was a less potent inducer of 2-AA mutagenicity at all time points, whereas DEP-exposed S9 was less potent than control saline at 3 and 7 days but not 1 day post-exposure. At 3 days post-exposure, DEP- or CB-exposed lung S9 did not significantly affect the mutagenicity of DEPE or 1-NP, when compared to the controls. The mutgenicity of 2-AA, 2-AF, 1-NP, and DEPE were significantly decreased in the presence of inhibitors for CYP1A1 (alpha-naphthoflavone) or CYP2B (metyrapone), but markedly enhanced by CYP1A1 or CYP2B1 supersomes with all the cofactors, suggesting that both CYP1A1 and CYP2B1 were responsible for mutagen activation. These results demonstrated that exposure of rats to DEP or CB altered metabolic activity of lung S9 and S9 metabolic activity dependent mutagen activation. The bioactivation of mutagens are metabolic enzyme- and substrate-specific, and both CYP1A1 and CYP2B1 play important roles in pulmonary mutagen activation.

Time-dependent apoptosis of alveolar macrophages from rats exposed to bleomycin: involvement of tnf receptor 2

Tumor necrosis factor-alpha (TNF-a) is produced by alveolar macrophages (AM) in response to bleomycin (BLM) exposure. This cytokine has been linked to BLM-induced pulmonary inflammation, an early drug effect, and to lung fibrosis, the ultimate toxic effect of BLM. The present study was carried out to study the time dependence of apoptotic signaling pathways and the potential roles of TNF receptors in BLM-induced AM apoptosis. Male Sprague-Dawley rats were exposed to saline or BLM (1 mg/kg) by intratracheal instillation. At 1, 3, or 7 d postexposure, AM were isolated by bronchoalveolar (BAL) lavage and evaluated for apoptosis by ELISA. The release of cytochrome c from mitochrondria, the activation of caspase-3, -8, and -9, the cleavage of nuclear poly(ADP-ribose) polymerase (PARP), and the expression of TNF receptors (TNF-R1/p55 and TNF-R2/p75), TNF-R-associated factor 2 (TRAF2), and cellular inhibitor of apoptosis 1 (c-IAP1) were determined by immunoblotting. The results showed that BLM exposure induced AM apoptosis, with the highest apoptotic effect occurring at 1 d after exposure and gradually decreasing at 3 and 7 d postexposure, but still remaining significantly above the control level. The maximal translocation of cytochromec from mitochondria into the cytosol was observed at 1 d postexposure, whereas the activation of caspase-9 and caspase-3 and caspase-3-dependent cleavage of PARP was found to reach a peak level at 3 d postexposure. BLM exposure had no marked effect on AM expression of TNF-R1 or caspase-8 activation, but significantly increased the expression of TNF-R2 that was accompanied by a rise in c-IAP1 and a decrease in TRAF2. This induction of TNF-R2 by BLM was significant on d 1 and increased with greater exposure time. In vitro studies showed that pretreatment of naive AM with a TNF-R2 antibody significantly inhibited BLM-induced caspase-3 activity and apoptosis. These results suggest that BLM-induced apoptosis involves multiple pathways in a time-dependent manner. Since maximal BLM-induced AM apoptosis (1 d postexposure) preceded maximal changes in caspase-9 and -3 (3 d postexposure), it is possible that a caspase-independent mechanism is involved in this initial response. These results indicate that the sustained expression of TNF-R2 in AM by BLM exposure may sensitize these cells to TNF-a-mediated toxicity.

Effects of paving asphalt fume exposure on genotoxic and mutagenic activities in the rat lung

Asphalt fumes are complex mixtures of aerosols and vapors containing various organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Previously, we have demonstrated that inhalation exposure of rats to asphalt fumes resulted in dose-dependent induction of CYP1A1 with concomitant down-regulation of CYP2B1 and increased phase II enzyme quinone reductase activity in the rat lung. In the present study, the potential genotoxic effects of asphalt fume exposure due to altered lung microsomal enzymes were studied. Rats were exposed to air or asphalt fume generated under road paving conditions at various concentrations and sacrificed the next day. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage and examined for DNA damage using the comet assay. To evaluate the systemic genotoxic effect of asphalt fume, micronuclei formation in bone marrow polychromatic erythrocytes (PCEs) was monitored. Lung S9 from various exposure groups was isolated from tissue homogenates and characterized for metabolic activity in activating 2-aminoanthracene (2-AA) and benzo[a]pyrene (BaP) mutagenicity using the Ames test with Salmonella typhimurium YG1024 and YG1029. This study showed that the paving asphalt fumes significantly induced DNA damage in AM, as revealed by DNA migration in the comet assay, in a dose-dependent manner, whereas the micronuclei formation in bone marrow PCEs was not detected even at a very high exposure level (1733 mg h/m3). The conversion of 2-AA to mutagens in the Ames test required lung S9-mediated metabolic activation in a dose-dependent manner. In comparison to the controls, lung S9 from rats exposed to asphalt fume at a total exposure level of 479+/-33 mg h/m3 did not significantly enhance 2-AA mutagenicity with either S. typhimurium YG1024 or YG1029. At a higher total asphalt fume exposure level (1150+/-63 mg h/m3), S9 significantly increased the mutagenicity of 2-AA as compared to the control. However, S9 from asphalt fume-exposed rats did not significantly activate the mutagenicity of BaP in the Ames test. These results show that asphalt fume exposure, which significantly altered both phases I and II metabolic enzymes in lung microsomes, is genotoxic to AM and enhances the metabolic activation of certain mutagens through altered S9 content.

Diesel exhaust particle-induced alterations of pulmonary phase I and phase II enzymes of rats

Although diesel exhaust particles (DEP) are known to produce pulmonary disorders, the xenobiotic metabolic pathways associated with DEP detoxification and bioactivation remain unclear. In this study, the effect of acute exposure of DEP on phase I and phase II enzymes of rat lung was investigated. Intratracheal administration of DEP produced an induction of cytochrome P-450 (CYP) 1A1 enzyme protein and activity at 1 d postexposure, with the enzyme level returning to control at 5 d postexposure. On the other hand, carbon black (CB), a particle control, did not show any induction of CYP1A1 protein or enzyme activity. However, both DEP and CB significantly decreased CYP2B1 protein and enzyme activity at 1 d postexposure. The decrease in CYP2B1 enzyme protein and activity by DEP or CB treatment was observed up to 7 d postexposure. DEP and CB treatments also significantly attenuated glutathione S-transferase (GST)-pi protein at 1 d postexposure. Both DEP and CB at 35 mg/kg significantly decreased the activities of GST and catalase at 1 and 7 d postexposure. DEP, but not CB, significantly induced quinone reductase (QR) activity at 7 d postexposure. This study suggests that DEP may induce CYP1A1 and QR enzymes via a chemical effect, while the carbonaceous core may be involved in the attenuation of CYP2B1, GST, and catalase proteins and enzyme activities.

Alteration of pulmonary cytochrome p-450 system: effects of asphalt fume condensate exposure

Exposure to asphalt fumes is a health concern due to the presence of polycyclic aromatic compounds (PACs) in asphalt. Bioactivation of many PACs requires metabolism by the cytochrome P-450 (P-450) system. The objective of this study was to evaluate the effects of exposure of rats to asphalt fume condensate (AFC), collected at the top of a paving asphalt storage tank, on the pulmonary microsomal P-450 system and to determine the genotoxic effects of such exposure. Male Sprague-Dawley rats were intratracheally instilled with saline or with 0.45, 2.22, or 8.88 mg/kg AFC for 3 consecutive days and sacrificed the following day. Lung microsomes were isolated by differential centrifugation of lung homogenates. Microsomal protein level, NADPH cytochrome c reductase activity, and the activities and protein levels of cytochrome P-450 isozymes CYP1A1 and CYP2B1 were monitored to assess the effects of AFC exposure on pulmonary P-450. The activities of CYP2B1 and CYP1A1 were determined by monitoring xenobiotic metabolism of 7-pentoxyresorufin and 7-ethoxyresorufin, respectively. CYP2B1 and CYP1A1 levels were determined by immunochemical analysis. Micronucleus (MN) formation in bone-marrow polychromatic erythrocytes (PCEs) was determined to assess the genotoxic effects of AFC exposure. The results showed that exposure of rats to AFC did not significantly affect total cytochrome P-450 content or cytochrome c reductase activity in the lung. CYP2B1 levels and enzyme activity were not significantly affected by AFC exposure. In contrast, CYP1A1 levels and activity were significantly increased in microsomes isolated from AFC-exposed lungs. Increased MN formation was observed only in high-dose AFC-exposed bone marrow PCEs. These results demonstrate that AFC exposure induced CYP1A1 activity and increased the enzyme levels of CYP1A1 in lung microsomes, suggesting that AFC exposure may alter metabolism of PACs by the cytochrome P-450 system in the lung. Alteration of cytochrome P-450 metabolism of PACs may contribute to the AFC-induced genotoxic effects demonstrated as MN formation.

Effect of exposure to diesel exhaust particles on the susceptibility of the lung to infection

There are at least three mechanisms by which alveolar macrophages play a critical role in protecting the lung from bacterial or viral infections: production of inflammatory cytokines that recruit and activate lung phagocytes, production of antimicrobial reactive oxidant species, and production of interferon (an antiviral agent). In this article we summarize data concerning the effect of exposure to diesel exhaust particles on these alveolar macrophage functions and the role of adsorbed organic chemicals compared to the carbonaceous core in the toxicity of diesel particles. In vitro exposure of rat alveolar macrophages to diesel exhaust particles decreased the ability of lipopolysaccharide (LPS), a bacterial product] to stimulate the production of inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha). Methanol extract exhibited this potential but methanol-washed diesel particles did not. Exposure of rats to diesel exhaust particles by intratracheal instillation also decreased LPS-induced TNF-alpha and IL-1 production from alveolar macrophages. In contrast, carbon black did not exhibit this inhibitory effect. Exposure of rats to diesel exhaust particles by inhalation decreased the ability of alveolar macrophages to produce antimicrobial reactive oxidant species in response to zymosan (a fungal component). In contrast, exposure to coal dust increased zymosan-stimulated oxidant production. In vivo exposure to diesel exhaust particles but not to carbon black decreased the ability of the lungs to clear bacteria. Inhalation exposure of mice to diesel exhaust particles but not to coal dust depressed the ability of the lung to produce the antiviral agent interferon and increased viral multiplication in the lung. These results support the hypothesis that exposure to diesel exhaust particles increases the susceptibility of the lung to infection by depressing the antimicrobial potential of alveolar macrophages. This inhibitory effect appears to be due to adsorbed organic chemicals rather than the carbonaceous core of the diesel particles.

Effect of age on respiratory defense mechanisms: pulmonary bacterial clearance in Fischer 344 rats after intratracheal instillation of Listeria monocytogenes

STUDY OBJECTIVES

To examine the lung defense mechanisms of both young and aged rats before and after pulmonary challenge with a bacterial pathogen.

DESIGN

Male Fischer 344 rats, either 2.5 months or 20 months of age, were intratracheally inoculated with 5 x 10(3), 5 x 10(4), or 5 x 10(5) Listeria monocytogenes, and the effects on mortality, lung inflammation, pulmonary bacterial clearance, alveolar macrophage (AM) function, and T-lymphocyte characterization were determined.

MEASUREMENTS AND RESULTS

In noninfected control animals, the older rats had lower numbers of AMs on lavage and a lower percentage of total T, CD4+, and CD8+ cells. No difference was observed between noninfected young and old rats in AM function, assessing both chemiluminescence and nitric oxide (NO) production. After bacterial challenge, aged rats exhibited an increase in mortality, pulmonary infection, and edema, and lung lesions, which were more extensive than those observed in the younger rats. Interestingly, AM chemiluminescence was enhanced, while AM NO, a highly important antibacterial defense product, was abrogated in the aged rats as compared to the young rats.

CONCLUSIONS

This study demonstrated that advanced age is associated with alterations in lung defense mechanisms and increased susceptibility to pulmonary bacterial infection marked by elevated mortality, slowed pulmonary bacterial clearance, and altered AM function, specifically a decrease in NO production. These observations are indicative of reduced pulmonary defense function in an older population of rats.

Effect of silica inhalation on the pulmonary clearance of a bacterial pathogen in Fischer 344 rats

Silica inhalation predisposes workers to bacterial infection and impairments in pulmonary defense function. In this study, we evaluated the effect of pre-exposure to silica on lung defense mechanisms by use of a rat pulmonary Listeria monocytogenes infection model. Male Fischer 344 rats were exposed by inhalation to filtered air or silica (15 mg/m3 x 6 h/day x 5 days/wk). After 21 or 59 days of silica exposure, the rats were inoculated intratracheally with 5 x 10(3) L. monocytogenes. At 0 (noninfected controls), 3, and 7 days after infection, the left lungs were removed, homogenized, and the number of viable L. monocytogenes was counted after an overnight culture at 37 degrees C. Bronchoalveolar lavage (BAL) was performed on the right lungs. Alveolar macrophages (AM) were collected, and the AM production of chemiluminescence (CL), an index of reactive oxygen species generation, was measured. The number of lavagable neutrophils (PMNs) and acellular BAL lactate dehydrogenase (LDH) activity were determined as indices of inflammation and injury, respectively. Pre-exposure to silica for 59 days caused substantial increases in PMN number and LDH activity compared with the air controls, whereas silica inhalation for both 21 and 59 days significantly enhanced the pulmonary clearance of L. monocytogenes compared with air controls. Dramatic elevations were also observed in zymosan- and phorbol myristate acetate (PMA)-stimulated CL production by lung phagocytes recovered from rats pre-exposed to silica for 59 days. These results demonstrate that short-term exposure to inhaled silica particles activates lung phagocytes, as evidenced by increases in reactive oxygen species. This up-regulation in the production of antimicrobial oxidants is likely responsible for the enhancement in pulmonary clearance of L. monocytogenes observed with short-term silica inhalation.

Diesel exhaust particles suppress macrophage function and slow the pulmonary clearance of Listeria monocytogenes in rats

In this study, we tested the hypothesis that exposure to diesel exhaust particles (DEP) may increase susceptibility of the host to pulmonary infection. Male Sprague-Dawley rats received a single dose of DEP (5 mg/kg), carbon black (CB, 5 mg/kg), or saline intratracheally. Three days later, the rats were inoculated intratracheally with approximately 5,000 Listeria monocytogenes and sacrificed at 3, 5, and 7 days postinfection, and we determined the number of viable Listeria in the left lobe of lungs. The remaining lungs underwent bronchoalveolar lavage (BAL) and the retrieved BAL cells were identified and counted. Luminol-dependent chemiluminescence, a measure of reactive oxygen species (ROS) formation, generated by BAL cells was monitored and the levels of nitric oxide and tumor necrosis factor (TNF)-[alpha] produced by macrophages in culture were determined. At 7 days postinfection, we excised the lung-draining lymph nodes and phenotyped the lymphocyte subpopulations. Exposure of rats to DEP, but not to CB, decreased the clearance of Listeria from the lungs. Listeria-induced generation of luminol-dependent chemiluminescence by pulmonary phagocytes decreased by exposure to DEP but not CB. Similarly, Listeria-induced production of NO by alveolar macrophages was negated at 3, 5, and 7 days after inoculation in DEP-exposed rats. In contrast, CB exposure had no effect on Listeria-induced NO production at 3 days after infection and had a substantially smaller effect than DEP at later days. Exposure to DEP or CB resulted in enlarged lung-draining lymph nodes and increased the number and percentage of CD4(+) and CD8(+) T cells. These results showed that exposure to DEP decreased the ability of macrophages to produce antimicrobial oxidants in response to Listeria, which may play a role in the increased susceptibility of rats to pulmonary infection. This DEP-induced suppression is caused partially by chemicals adsorbed onto the carbon core of DEP, because impaired macrophage function and decreased Listeria clearance were not observed following exposure to CB.

Diesel exhaust particles suppress macrophage function and slow the pulmonary clearance of Listeria monocytogenes in rats

In this study, we tested the hypothesis that exposure to diesel exhaust particles (DEP) may increase susceptibility of the host to pulmonary infection. Male Sprague-Dawley rats received a single dose of DEP (5 mg/kg), carbon black (CB, 5 mg/kg), or saline intratracheally. Three days later, the rats were inoculated intratracheally with approximately 5,000 Listeria monocytogenes and sacrificed at 3, 5, and 7 days postinfection, and we determined the number of viable Listeria in the left lobe of lungs. The remaining lungs underwent bronchoalveolar lavage (BAL) and the retrieved BAL cells were identified and counted. Luminol-dependent chemiluminescence, a measure of reactive oxygen species (ROS) formation, generated by BAL cells was monitored and the levels of nitric oxide and tumor necrosis factor (TNF)-[alpha] produced by macrophages in culture were determined. At 7 days postinfection, we excised the lung-draining lymph nodes and phenotyped the lymphocyte subpopulations. Exposure of rats to DEP, but not to CB, decreased the clearance of Listeria from the lungs. Listeria-induced generation of luminol-dependent chemiluminescence by pulmonary phagocytes decreased by exposure to DEP but not CB. Similarly, Listeria-induced production of NO by alveolar macrophages was negated at 3, 5, and 7 days after inoculation in DEP-exposed rats. In contrast, CB exposure had no effect on Listeria-induced NO production at 3 days after infection and had a substantially smaller effect than DEP at later days. Exposure to DEP or CB resulted in enlarged lung-draining lymph nodes and increased the number and percentage of CD4(+) and CD8(+) T cells. These results showed that exposure to DEP decreased the ability of macrophages to produce antimicrobial oxidants in response to Listeria, which may play a role in the increased susceptibility of rats to pulmonary infection. This DEP-induced suppression is caused partially by chemicals adsorbed onto the carbon core of DEP, because impaired macrophage function and decreased Listeria clearance were not observed following exposure to CB.

Subchronic silica exposure enhances respiratory defense mechanisms and the pulmonary clearance of Listeria monocytogenes in rats

Both Listeria monocytogenes infection and silica exposure have been shown to significantly alter immune responses. In this study, we evaluated the effect of preexposure to silica on lung defense mechanisms using a rat pulmonary L. monocytogenes infection model. Male Sprague-Dawley rats were instilled intratracheally with saline (vehicle control) or silica using either an acute treatment regimen (5 mg/kg; 3 days) or a subchronic treatment protocol (80 mg/kg; 35 days). At 3 or 35 days after silica instillation, the rats were inoculated intratracheally with either approximately 5000 or 500,000 L. monocytogenes. At 3, 5, and 7 days postinfection, the left lung was removed, homogenized, and cultured on brain heart infusion agar at 37 degrees C. The numbers of viable L. monocytogenes were counted after an overnight incubation. Bronchoalveolar lavage (BAL) was performed on the right lungs, and BAL cell differentials, acellular lactate dehydrogenase (LDH) activity and albumin content were determined. Alveolar macrophage (AM) chemiluminescence (CL) and phagocytosis were assessed as a measure of macrophage function. Lung-associated lymph nodes were removed, and lymphocytes were recovered and differentiated. Preexposure to silica significantly increased the pulmonary clearance of L. monocytogenes as compared to saline controls. Exposure to silica caused significant increases in BAL neutrophils, LDH and albumin, and lymph-nodal T cells and natural killer (NK) cells in infected and noninfected rats. CL and phagocytosis were also elevated in silica-treated rats. In summary, the results demonstrated that exposure of rats to silica enhanced pulmonary immune responses, as evidenced by increases in neutrophils, NK cells, T lymphocytes, and macrophage activation. These elevations in pulmonary immune response are likely responsible for the increase in pulmonary clearance of L. monocytogenes observed with preexposure to silica.

Effects of asphalt fume condensate exposure on acute pulmonary responses

OBJECTIVE

The present study was carried out to characterize the effects of in vitro exposure to paving asphalt fume condensate (AFC) on alveolar macrophage (AM) functions and to monitor acute pulmonary responses to in vivo AFC exposure in rats.

METHODS

For in vitro studies, rat primary AM cultures were incubated with various concentrations of AFC for 24 h at 37 degrees C. AM-conditioned medium was collected and assayed for lactate dehydrogenase (LDH) as a marker of cytotoxicity. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) production were assayed in AM-conditioned medium to monitor AM function. The effect of AFC on chemiluminescence (CL) generated by resting AM or AM in response to zymosan or PMA stimulation was also determined as a marker of AM activity. For in vivo studies, rats received either (1) a single intratracheal (IT) instillation of saline, or 0.1 mg or 0.5 mg AFC and were killed 1 or 3 days later; or (2) IT instillation of saline, or 0.1, 0.5, or 2 mg AFC for three consecutive days and were killed the following day. Differential counts of cells harvested by bronchoalveolar lavage were measured to monitor inflammation. Acellular LDH and protein content in the first lavage fluid were measured to monitor damage. CL generation, TNF-alpha and IL-1 production by AM were assayed to monitor AM function.

RESULTS

In vitro AFC exposure at <200 microg/ml did not induce cytotoxicity, oxidant generation, or IL-1 production by AM, but it did cause a small but significant increase in TNF-alpha release from AM. In vitro exposure of AM to AFC resulted in a significant decline of CL in response to zymosan or PMA stimulation. The in vivo studies showed that AFC exposure did not induce significant neutrophil infiltration or alter LDH or protein content in acellular lavage samples. Macrophages obtained from AFC-exposed rats did not show significant differences in oxidant production or cytokine secretion at rest or in response to LPS in comparison with control macrophages.

CONCLUSIONS

These results suggest that: (1) in vitro AFC exposure did not adversely affect cell viability or induce the release of high levels of inflammatory cytokines or oxidants; and (2) exposure of rats to AFC did not cause acute pulmonary inflammation or injury, and did not significantly alter AM functions.

Effects of diesel exhaust particles (DEP), carbon black, and silica on macrophage responses to lipopolysaccharide: evidence of DEP suppression of macrophage activity

The effects of diesel exhaust particle (DEP) exposure on alveolar macrophage (AM) response to ex vivo and in vivo lipopolysaccharide (LPS) challenge were determined by monitoring LPS-stimulated production of interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha). The roles of the insoluble particulate and the organic compounds of DEP in altering pulmonary responses were evaluated by comparing the DEP-induced pulmonary responses to those of carbon black (CB), a carbonaceous particle with few adsorbed organic compounds, or to silica, a known pneumotoxic dust. Male Sprague-Dawley rats were exposed to a single intratracheal dose (5 or 35 mg/kg body weight) of DEP, CB, or silica, or to saline vehicle. Rats were sacrificed 1, 3, or 7 d postexposure. To study the responsiveness to the bacterial product LPS, AM isolated from particle-exposed rats were challenged ex vivo with LPS (0.1 microg/10(6) AM) and LPS-stimulated cytokine release was monitored. In addition, rats were exposed intratracheally to a single dose of DEP (5 mg/kg) and 3 d later exposed in vivo to 1 mg/kg LPS for 3 h prior to measurement of cytokine production by AM. DEP exposure resulted in neutrophil infiltration and elevated levels of albumin and lactate dehydrogenase (LDH) activity in the bronchoalveolar lavage fluid; these responses were not substantially different from those elicited by CB or silica exposure. AM from DEP-exposed rats showed increased spontaneous production of IL-1, but not TNF-alpha, while the opposite was true for CB or silica. Upon ex vivo challenge with LPS, AM from DEP-exposed rats showed a significant decrease in the secretion of TNF-alpha and, to a lesser extent, IL-1, compared to the sum of the DEP and LPS effects. In contrast, AM from CB- or silica-exposed rats did not show this decreased responsiveness to subsequent LPS challenge. This inhibitory action of DEP on LPS-stimulated AM production of IL-1 and TNF-alpha was further confirmed by the results obtained from rats exposed to both DEP and LPS in vivo. In summary, these results indicate that while DEP, CB, and silica all induce pulmonary inflammatory responses due to particle stimulation, only DEP suppress AM cytokine release in response to LPS stimulation. The contrasting cellular response with respect to DEP and CB exposures may be due to the presence of adsorbed organic compounds on DEP, which may contribute to the increased susceptibility of hosts to pulmonary infections after DEP exposure.

Use of tetrandrine to differentiate between mechanisms involved in silica-versus bleomycin-induced fibrosis

Animals exposed to silica or bleomycin (BLM) develop pulmonary fibrosis. Tetrandrine (TT) has been shown to inhibit stimulant-induced macrophage respiratory burst and effectively reduce silica-induced lung injury. The present study employed TT as a probe to assess the differences in mechanisms involved in silica- and BLM-induced pulmonary responses. Rats received a single intratracheal instillation of silica (40 mg/rat, sacrificed 4 wk postexposure) or BLM (1 mg/kg or approximately 0.25 mg/rat, sacrificed up to 2 wk postexposure). TT was administered orally at 18 mg/kg, 3 times/wk for desired time periods beginning 5 d before silica or BLM exposure. Both the silica and BLM exposures resulted in a significant increase in lung weight, total protein, lactate dehydrogenase (LDH), and phospholipids (PL) content in the acellular fluid from the first lavage, and hydroxyproline content in the lung tissue. Alveolar macrophages (AM) isolated from rats exposed to silica or BLM exhibited significant increases in secretion of interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-alpha), and transforming growth factor beta (TGF-beta). TT treatment significantly lowered the silica- or BLM-induced increase in lung weight, while marginally reducing the release of IL-1 and TNF-alpha by AM. TT, however, markedly inhibited the silica-induced increase in the acellular protein, LDH and PL, hydroxyproline content, and the production of TGF-beta by AM but had no marked effect on these same parameters in BLM-exposed rats. Histological examination of rats exposed to BLM for 14 d showed pulmonary inflammation and fibrosis. TT treatment had only a small effect on limiting the extent of these lesions and did not significantly affect their severity. In summary, data indicate that many inflammatory and fibrotic effects of in vivo silica exposure are substantially attenuated by TT, whereas the stimulation by BLM is only marginally affected by this drug. Since TT acts to attenuate AM-mediated reactions, these results suggest that AM may play a pivotal role in silica-induced fibrotic development and may be less involved in the pathogenesis of BLM-induced fibrosis.

Augmentation of pulmonary reactions to quartz inhalation by trace amounts of iron-containing particles

Fracturing quartz produces silica-based radicals on the fracture planes and generates hydroxyl radicals (.OH) in aqueous media. .OH production has been shown to be directly associated with quartz-induced cell damage and phagocyte activation in vitro. This .OH production in vitro is inhibited by desferrioxamine mesylate, an Fe chelator, indicating involvement of a Fenton-like reaction. Our objective was to determine if Fe contamination increased the ability of inhaled quartz to cause inflammation and lung injury. Male Fischer 344 rats were exposed 5 hr/day for 10 days to filtered air, 20 mg/m3 freshly milled quartz (57 ppm Fe), or 20 mg/m3 freshly milled quartz contaminated with Fe (430 ppm Fe). High Fe contamination of quartz produced approximately 57% more reactive species in water than quartz with low Fe contamination. Compared to inhalation of quartz with low Fe contamination, high Fe contamination of quartz resulted in increases in the following responses: leukocyte recruitment (537%), lavageable red blood cells (157%), macrophage production of oxygen radicals measured by electron spin resonance or chemiluminescence (32 or 90%, respectively), nitric oxide production by macrophages (71%), and lipid peroxidation of lung tissue (38%). These results suggest that inhalation of freshly fractured quartz contaminated with trace levels of Fe may be more pathogenic than inhalation of quartz alone.

Modification of alveolar macrophage function with bis-basic ethers of fluorene and fluoren-9-substituted derivatives

Bis-basic ethers of fluorene and fluoren-9-substituted derivatives such as tilorone have been reported to inhibit silica-induced fibrosis in rats. The potential antifibrotic potency of 2,7-bis(diethylamino)ethoxy fluorene (F-9-H,H), fluorenone (F-9-one), fluorenoxime (F-9-oxime), and fluorenol (F-9-ol) was F-9-oxime > F-9-one approximately F-9-H,H >> F-9-ol. Since the release of reactive oxygen species and growth factors from alveolar macrophages (AM) in response to silica exposure has been linked to the development of pulmonary fibrosis, the present study was carried out to determine the inhibitory effects of these compounds on rat AM activity in vitro. The following parameters were monitored: (1) cellular viability; (2) zymosan-induced respiratory burst activity (superoxide and hydrogen peroxide release, chemiluminescence, and oxygen consumption) of AM; (3) drug binding to AM; and (4) lipopolysaccharide (LPS)-stimulated interleukin-1 (IL-1) release from AM. The bis-basic ethers, at 40 microM, did not affect cell viability when incubated with AM for 30 min, but significantly inhibited zymosan-induced macrophage respiratory burst activity. The inhibitory effect of these agents was F-9-oxime > F-9-one approximately F-9-H,H >> F-9-ol. Binding of these drugs to AM was time and dose dependent, and exhibited the following binding affinity: F-9-oxime > F-9-one > F-9-H,H > F-9-ol. F-9-oxime was shown to inhibit LPS-stimulated IL-1 release by AM in a dose-dependent manner. This inhibition of IL-1 release by AM cannot be explained as a decrease in viability. In addition, these drugs were also shown to impair human fibroblast proliferation in response to serum stimuli without impairing cell viability. These results indicate a positive correlation between drug binding to AM or other cell types and their inhibitory effects on cellular activities including oxygen consumption, superoxide release, hydrogen peroxide secretion, chemiluminescence, IL-1 release, and proliferation. The ability of these bis-basic ethers to modify AM and fibroblast functions in vitro suggests that further investigation of their reported antifibrotic potency in vivo is warranted.

Organic dust exposure from compost handling: response of an animal model

The objective of this investigation was to elucidate the pulmonary responses of an animal model to dust generated from leaf/wood compost which had caused a severe case of acute respiratory illness in an individual. Guinea pigs were exposed for 4 hr to 30 mg/m3 of aerosolized leaf/wood compost dust. Inhalation resulted in significant cellular activation and changes in pulmonary mechanics. Maximal elevation in breathing rate (increases 36%) was observed 12-18 hr postexposure. Similarly, maximal granulocyte infiltration (increases 1,600%) and activation of alveolar macrophages (increases 65%) occurred 18 hr postexposure. In contrast, maximal airway obstruction (increases 120%) occurred immediately after exposure and returned toward normal (increases 53%) by 18 hr postexposure. In several respects, the airway obstruction and pulmonary inflammation described in the animal model were comparable to the human response to compost dust. Therefore, this animal model may be useful in predicting the potential respiratory hazard associated with exposure to various organic dusts.

Exposure of rats to hyperoxia: alteration of lavagate parameters and macrophage function

Exposure of rats to hyperoxia (100% oxygen for 64 h) resulted in striking alterations in the properties of samples obtained by bronchoalveolar lavage. The yield of neutrophils, lymphocytes, and red blood cells was increased, while the number of harvested alveolar macrophages decreased. The acellular lavage fluid level of protein was elevated, indicating lung damage. However, acellular phospholipid levels were unchanged. The ability of alveolar macrophages to produce reactive forms of oxygen in response to zymosan was significantly decreased by oxygen exposure. This impaired function was not fully explained by a decrease in viability of these phagocytes. In contrast, stimulant-induced chemiluminescence was elevated after hyperoxia. This rise was not due to a change in cellular antioxidant levels or to a discernible increase in arachidonic acid metabolites. However, it was associated with increased cellular lipid peroxidation.